Prefill valve for hydraulic presses



April 4, 1939. E. CANNON PREF ILL VALVE FOR HYDRAULIC PRESSES Filed Jan.2l 1957 3 Sheets-Sheet l INVENTOR April 4, 1939. E. CANNON PREFILL VALVE FOR HYDRAULIC PRESSES Filed Jan. 21, 1957 3 Sheefis-Sheet 2INVENTOB W R YS.

April 4, 1939. E. CANNON 2,152,870

I v PREFILL VALVE FOR HYDRAULIC PRESSES Filed Jan. 21, 1937 3Sheets-Sheet 5 INVENTOR Patented Apr. 4, 1939 UNITED STATES PATENTOFFICE PREFILL VALVE FOR- HYDRAULIC PRESSES Application January 21,1937, Serial No. 121,528

19 Claims.

This invention relates to improvements in prefill valves (otherwiseknown as surge valves) for hydraulic presses, which valves are employedfor permitting the rapid filling and exhaustion of the ram chamber of ahydraulic press with oil or otherfluid during the operation thereof.

In the practical operation of a hydraulic press the filling of the ramchamber, prior to the establishment of a relatively high workingpressure,therein, ordinarily takes place as a result of suction which is set upin said chamber by the advance of the ram into initial engagement withthe material being processed. Such advance of the ram may beaccomplished by various means. Hydraulic pressure may, for example, beapplied directly to the ram, for the said purpose in the mannerdescribed and illustrated in my co-pending application, Serial No.105,005, filed October 10, 1936 and issued as Patent No. 2,127,324 onAugust 16, '1938, or the advance of the main ram may be accomplished byindependent means, such, for example, as auxiliary hydraulic rams whichmay be arranged to coact directly with the platen or die carried at theouter end of the main ram.

The present invention is particularly advantageous as employed inprefill valves of the type which are .opened either by hydraulicpressure or by a spring, and are closed and held closed solely byhydraulic pressure. Such valves commonly havea valve element whichreciprocates within a valve chamber between an open position wherein itis clear of the main fluid inlet to the ram work chamber, whereby topermit a free flow or surge of fluid thereinto, and a closed positionwherein said element seats across and closes said inlet whereby topermit theestablishment of a relatively high working pressure within theram chamber; i In such hydraulically closed prefill valves, heretoioredeveloped, fluid, under pressure, p is intrbducedinto the valve chamberat the upper or'buter side of the'reciprocating valve element,

causing the latterto move to a closed position, whereuponworking-fpr'essure is established in said valve chamber and,"by onemeans or another, passed, through or by-passed around the reciprocatingvalve element into the prefilled ram chamber whereby toestablish thedesired working pressure therein and impose sufilcient force upon theram to' accomplish the desired work. I

In such valves the means for by-passing the pressure from the valvechamber into the ram chamber are so arranged that substantially uniformpressure is maintained in both said chambers while the valve is closed,and as the effeccause of the'necessarily large area of the top of thevalve element, the speed of operation of the press is substantiallylimited to the speed at which the valve chamber may be completely filledand exhausted. While, in actual practice, the stroke of such hydraulicpresses is completed in a relatively short time, it will nevertheless beappreciated that any considerable increase in the working speed of thepress yields consider-, able economies in operation.

An important object of my present invention is the provision of aprefill valve, of the general character hereinbefore referred to, whichmay be hydraulically closed by the more rapid introduction of asubstantially lesser volume of fluid than is required in previouslydeveloped valves of similar dimensions, resulting in substantial economyin operation of such valves and associated hydraulic presses.

A further object of my invention is the provision of a prefill valve, ofthe general character referred to, wherein the pressure above thereciprocating valve element, holding the latter closed, is releasedsubstantially simultaneously with the pressure in the ram chamber belowsaid valve element, when thevalveis opened, whereby to alleviate harmfulstructural stresses which otherwise maybe encountered in operation.

A still further object ofmy invention is the provision of a prefillvalve, of the general character referred to, in which the displacementof fluid from above the valve element is somewhat retarded, as thelatter is forced upwardly or outwardly to its open position, whereby tocushion the'outward movement of said element and thus afford a furthersafeguard against harmful structuralstresses. I

These and otherobiects are accomplished by my invention, which, forillustrative purposes, is

described herein and illustrated in the accompanying drawings asembodied in a vertically disposed preflll valve, although such valvesmay also, within the invention, be horizontally disposed, or may bearranged in an inverted position'or in various oblique positions.

Referring to the drawings:

Figure 1 is a substantially central vertical section of a prefill valveembodying my invention.

Fig. 2 is a horizontal section substantially on the line 2-2 of Fig. 1.

Fig. 3 is a substantially central vertical section of a prefill valveembodying a modification of my invention.

Fig. 4 is a horizontal section substantially on the line 4-4 of Fig. 3.

Fig. 5 is a substantially central vertical section of a prefill valveembodying a further modification of my invention.

Fig. 6 is a horizontal section substantially on the line 6-6 of Fig. 5.

Fig. 7 is a substantially central vertical section of a prefill valveembodying a slight variation of the modification disclosed in Fig. 5.

My invention as illustrated in Figs. 1 and 2 is embodied in a prefillvalve in which the means for initially advancing the ram into engagementwith the material being processed are directly associated with the valvestructure, substantially as disclosed in my said co-pending application.In the embodiment illustrated in said figures, a substantiallycylindrical valve casing- H is secured to the upper end of a ramcylinder block l2 by bolts [3 which extend through holes in flanges orlugs I4 at the lower end of the valve casing and are threaded into theram cylinder block.

The valve casing II and the cylinder block l2, respectively, enclosecommunicating chambers l5 and Hi, the several parts of the formerchamber being hereinafter more fully described and more specificallycharacterized, and the latter chamber being hereinafter referred to as aram chamber. The upper end of chamber I5 is closed by a head I I whichis secured to the valve casing II by bolts l8.

A ram I9 is accurately fitted within the ram chamber l6 and is adaptedtobe reciprocated therewithin by hydraulic pressure. A reciprocatingvalve element or piston 20 is fitted within the chamber iii of the valvecasing and is adapted to be hydraulically reciprocated therewithinbetween a raised or open position as indicated in broken lines in Fig.1, and a lowered or closed position as indicated in full lines.

One or more surge ports 2| are provided near the lower end of the valvecasing II to permit fluid communication between a surge chamber I50, atthe lower end of the chamber l5,,-and a fluid tank 22 which is suitablymounted upon the ram cylinder block l2 and may enclose a substantialportion of the prefill valve.

The upper end of the ram cylinder block I2 is shouldered inwardly toform a neck 23 within which an annular valve seat element 24 is tightlyand accurately fitted, said valve seat element and,

the periphery of the lower face of the piston 20 being complementallybeveled to form. seating surfaces which coact when the piston 20 is inits closed position whereby to break the fluid communication betweenthe. surge chamber [5a and the ram chamber l6.

An inwardly extending annular shoulder 25 is formed integrally with thevalve casing H at a point immediately above the surge ports 2| and aring Ila, which may be formed integrally with the head I1, is fittedaccurately within the upper end of the chamber l5, thus reducing thediameter of the said chamber toward the upper and lower ends thereof andproviding an intermediate portion of said chamber with a relativelygreater diameter.

The reduced diameters of the chamber l5 are preferably similar at thering Ila and the shoulder 25, and the piston 20 is arranged to fitaccurately within and work within said ring and shoulder. The saidpiston is enlarged circumferentially, intermediate its ends, to form acircumferential shoulder 26 which fits accurately within the greaterdiameter of the chamber l5 and partly defines an annular valve closingchamber l5b above said shoulder 26 and an annularvalve-opening chamberI50, below said shoulder.

A port 21, served by a pipe 28, extends through the valve casing ll intothe extreme upper portion of the valve-closing chamber [5b to permitfilling and exhaustion of said chamber, and,

similarly, a port 29 and pipe 30 are provided at the extreme lowerportion of the valve-opening chamber l5c to permit filling andexhaustion thereof. It will be perceived from Fig. 1, that the severalparts described are so arranged and proportioned that the volumes of thechambers 15b and I50 vary inversely with the reciprocation of the piston20, and, further, that the ports 21 and 29 are at all times uncovered attheir inner ends and afford unrestricted fluid passages into thechambers 15b and I50, respectively, during the entire stroke of thepiston 20.

Means are provided in the piston 20 for establishing fluid communicationbetween the annular valve-closing chamber lib and the ram chamber IS.The said means comprise an axial duct 3| extending from the bottom ofthe piston 20 almost to the top thereof, and a lateral passage 32extending from the duct 3|, and through the side wall of the piston 20at a point at or near the top of the said duct, the passage 32, further,being so disposed that its outer end is uncovered, by the ring Ha,-whereby to afford fluid communication between the duct 3| and thevalve-closing chamber I5b, when the piston is in its closed position.

Means for providing a regulated uni-directional flow of fluid downwardlythrough the duct 3| comprise a normally spring-closed check valve 33,arranged within said duct to seat against the under side of an annularshoulder 34 therein. The said check valve has an upwardly-extendingshank 35 around which extends a compression coil spring 36 seatingagainst the upper side of the shoulder 34, and a washer 3'I, retained onthe shank 35 by a nut 38 which is screwed onto the upper end of the saidshank. The upper end of said shank is suitably threaded to receive thenut 38 and to permit adjustment of the tension of the spring 36 byadjustment of the said' nut. A screw-plug 39 is screwed into the upperend of the duct- 3|, which, while preventing undesired fluidcommunication between the latter and the area above the top of thepiston 20, may nevertheless be easily unscrewed and removed to affordaccess to the nut 38 for adjustment purposes.

In the structure illustrated in Fig. 1, the means for advancing orlowering the ram into initial engagement with the material beingprocessed, comprises a rigid tube or pipe 39', which, at a reduced upperend thereof, is rigidly secured to the head I! by a nut 40 and extendssubstantially vertically and centrally through a suitable hole in thesaid head, and also through suitable bores in the piston 20 and the raml9, within which bores (particularly the bore in the ram) the tube 39'is accurately fitted to prevent fluid leaka'ge therearound. The tube 39'has a longitudinal passage 4| extending throughout the entire lengththereof and terminates in and opens into a quick advance chamber 42 inthe interior of the ram I9.

The details of the quick advance chamber 42 and of hydraulic means foractuating the ram I9 on its return stroke (not shown herein) may besimilar to comparable details disclosed in my said co-pendingapplication, but as the present invention does not depend on suchdetails, they have been omitted herefroin.

One or more axial passages 43 are provided in the piston 20 and afford arelatively unimpeded fluid communication between the area below thepiston 20 and the area I5d, above the said piston, said latter areabeing hereinafter referred to as a pressure-balancing chamber I501. Thepassages 43 are adapted to permit the filling and exhaustion of thechamber I5d and the size and number of such passages may be arranged toaccomplish the said purpose in a desired period of time, due regardbeing had, of course, for the viscosity of the fluid which is to beemployed in operating the press.

The pressure-balancing chamber I5d, and the 4 ram chamber I6, being influid communication with each other when the piston 20 is in its closedposition, will, at such times, be under uniform working pressures and asthe effective area of the top of the piston 20' is greater than theeffective area of the bottom thereof, it results that a preponderousforce on the top of the piston will hold it closed while such uniformpressure is maintained in the chambers I5d and I6.

An understanding of the operation of the device hereinbefore describedshould be helpful in fully understanding the invention and theadvantages thereof. Referring to Fig. 1, the cycle of operation may beconsidered as commencing with the ram I9 and the piston 2|] in their,uppermost positions, as indicated in broken lines, and with all thechambers, passages, and ducts hereinbefore referred to containing fluidat substantially atmospheric pressure. It should further be understoodthat the tank 22 contains a supply of fluid, at substantiallyatmospheric pressure, suflicient to provide for the operation of thedevice as hereinafter described.

With the ram I9 and the piston 20 in their uppermost positions, fluid isfirst introduced through the passage 4| in the tube 39 into the quickadvance chamber 42 in the ram, thus causing the latter to descendsufficiently to bring a die carried at the lower end thereof intoinitial engagement with the material being processed. The descent of theram I9 creates suction in the ram chamber I6, thus drawing fluid fromthe tank 22, through the surge ports 2 I, into the surge chamber I5a andthence into the ram chamber, so that with the substantial completion ofthe descent of the ram I9, the ram chamber I6, substantially enlarged bythe descent of the ram, is entirely occupied by fluid at substantiallyatmospheric pressure.

Fluid is then introduced into the valve-closing chamber I5b through theport 21, while the fluid in the valve-opening chamber I56 issimultaneously being exhausted through the port 29 (the said chambers.and their respective ports being so arranged and connected to a sourceof fluid under pressure that when the one chamber is being filled, theother is simultaneously being exhausted, and vice versa), thus causingthe piston 20 to descend to a closed position. While the piston 20descends, the pressure-balancing chamber I 5d above the piston increasesin volume, and as the said chamber is entirely closed, except for theaxial passages 43, there results an upward flow of fluid from the surgechamber |5a through said axial passages 43 and into thepressurebalancing chamber I5d, so that upon the piston reaching itsclosed position, the enlarged ram chamber I 6, the axial passages 43,and the enlarged pressure-balancing chamber Hill are all full of fluidat substantially uniform pressure.

With the descent of the piston 20, the lateral passage 32 has moved to apoint below the lower edge of the ring IIa, thus uncovering said lateralpassage and establishing fluid communication between the valve-closingchamber I51) and the upper end of the axial duct 3|, and continuedintroduction of fluid through the port 21, under pressure, causes thecheck valve 33 to open and establishes a suitable working pressure inthe ram chamber I6 and a similar pressure in the communicatingpressure-balancing chamber I5d, the pressure in said chambers beingraised sufliciently to enable the press to perform the desired work. Theeffective area of the piston 20 which is subjected to downward pressure,when the valve is closed, being greater than the effective area thereofsubjected to upward pressure, and all said areas being subjected to asubstantially uniform has been completed, the return stroke is accom-.

plished by simultaneously exhausting the valveclosing chamber I5bthrough the port 21 and introducing fluid under pressure through theport 29 into the valve-opening chamber I50, at the same time raising theram I9 by any suitable means which, for example, may be in the form of ahydraulic cylinder functioning directly with the said ram, as disclosedin my said co-pending application; the means for raising the ram,however, not being illustrated herein, as it forms no necessary part ofthe present invention.

When the valve-closing chamber |5b is exhausted and the high pressure isintroduced into the valve-opening chamber I50, the aggregate upwardhydraulic force being exerted against the underside of the shoulder 26on the piston and on the underside of the lower end of the piston isgreater than the downward hydraulic force being exerted upon the upperend of said piston. This predominant upward force causes the piston 20to move to its uppermost, or open, position, during which movement fluidfrom the pressurebalancing chamber I5d passes downwardly through theaxial passages 43, unites with the fluid being expelled from the ramwork chamber I6 and may pass out, in'part through the surge chamber |5aand the surge ports 2| into the tank 22,

It will be seen from the foregoing explanation that, in order to closethe prefill valve after the descent of the ram, it is only necessary tointroduce into the valve a relatively small-volume of fluid, equivalentto the difference between the volume'of the relatively smallvalve-closing chamber |5b when the piston is in a closed position andthe volume of said cylinder when the piston the time element involved inintroducing fluid into the chamber 15b, as stated, would besubstantially less than the time element involved in introducing fluidinto a relatively large hydraulic chamber provided at the top of thepiston.

This result has been accomplished by the present invention, in itsbroader aspects, by providing a valve-closing chamber which is of aminimum practical size suitable for effecting the closing of the valveand a separate chamber for approximately balancing the upward hydraulicforce imposed upon the piston when the ram is subjected to workingpressure. The structure, if desired, may be so arranged that thepressurebalancing chamber alone would not achieve such balancing effect,but it would then be essential that the downward force within thevalve-closing chamber sufficiently augment the downward force within thepressure-balancing chamber so that both said chambers would afford aneffective pressure balance whereby to hold the piston in its closedposition. Such an arrangement is illustrated in Fig. '7 and ishereinafter more fully described.

It will further be observed that the axial passages 43, in the piston,constitute means for rapidly filling the pressure-balancing chamber l5dwhile the piston is being moved to its closed position, thus obviatingthe necessity of providing means for filling said pressure-balancingchamber from the exterior of the valve structure.

It should also be apparent that, inasmuch as the chambers l5d and I6 arein fluid communication when the valve is closed, the pressure withinboth said chambers is simultaneously released at the instant the valveis opened, and hence, any structural stresses or shocks incident to therelease of pressure would be minimized and substantially distributed andabsorbed throughout the valve structure, and any possible harmfuleffects of such stresses or shocks would be substantially obviated.

Figs. 3 to 6, inclusive, illustrate prefill valves in which theprinciples involved in. effecting closure thereof are similar to thosehereinbefore described with reference to the structure disclosed in Fig.i, but spring means are provided for opening the valve, supplanting thevalve opening chamber I50 and the associated port 29 and pipe 30, asillustrated in Fig. 1. A further difference between the valves of Figs.3 to 6, inclusive, and Fig. 1 is that the former have no means directlyassociated therewith for advancing the ram into initial engagement withthe material being processed. The means for advancing the ram, in thestructures of said former figures, may be of any suitable type, such as,for example, independent hydraulic rams (not shown) which may bearranged to coact directly with. the die normally secured to the lowerend of the ram.

Referring to the structure illustrated in Fig. 3, a compression coilspring 44 is disposed about a reduced lower portion of the piston: 20,said spring seating at its lower end upon the valve seat element 24,and, at its upper end, against the under side of the shoulder 26 on thepiston, thus normally holdingthe latter in its raised or open position.The relatively high pressure introduced into the valve-closing chamberl5b is suflicient to close the valve against the compression of thespring 44, it being understood, of course, that the adustment of thetension of the spring 36 is such that the check valve 33 will not openuntil the valve is fully closed.

Only a single axial passage 43 is provided in the'structure asillustrated in Fig. 3, and a normally spring-closed retarding valve 45is mounted in an enlarged upper end of said passage, said valve beingadapted to retard the exhaustion of the pressure-balancing chamber I5don the opening stroke of the piston 20 while nevertheless permittingrapid filling of said chamber on the closing stroke of the piston.

. The retarding valve 45 is provided with a head 46, having a beveled,annular seating surface on the under side thereof coasting with acomplementally beveled seating surface at the lower end of an enlargedportion of the passage 43, as at 41. The retarding valve 45 also has ashank 48, extending downwardly into a narrow portion of the passage 43,with radial fingers 49 which coact with the wall of said passage toserve as guiding means for said valve.

The retarding valve 45 is held normally seated or closed by acompression coil spring 5|] disposed between said valve and a perforatescrew plug 5| which is screwed into the upper end of the passage 43 andis adapted to permit adjustmentof-the tension of the spring 50. Theperforations in said screw plug permit fluid to pass freelytherethroug-h in either direction. Similar nipples 52, which arecentrally disposed on the top and bottom, respectively, of the valve 45and the screw plug 5|, extend into the coil spring 50 whereby tomaintain the latter in axial alignment with said valve. An exhaustpassage 53 of relatively small diameter, extending through the head 46of 'the retarding valve, permits a relatively gradual exhaustion of thepressure-balancing chamber 15d while the valve is opening. To

the same end, it would be feasible, if desired, to provide an exhaustpassage in the form of a second axial passage 43, 'of relatively smalldiameter, in the structure of the piston 20, instead of the passage 53in the valve head 46.

It will be seen that, in the operation of a valve, according to Fig. 3,the retarding valve 45 would open upon the closing stroke of the piston20 whereby to permit the rapid filling of the pressure-balancing chamberl5d, but that onthe opening stroke of said piston the said retardingvalve would not open and the exhaustion of the chamber l5d could onlytake place quite slowly through the small exhaust passage 53. The fluidremaining in the chamber l5d during the relatively slow exhaustionthereof would thus serve as a cushion which would oppose the normaltendency of the compression spring 44 to throw the piston suddenlyupwardly and would thus obviate any undesirable shock which mightotherwise be encountered. The extent of this cushioning effect woulddepend, in a substantial degree, upon the diameter of the exhaustpassage 53 or its equivalent, and hence said passage may be suitablyproportioned to achieve a desired cushioning efiect.

Referring to the structure illustrated in Fig. 5, two or more stud bolts54 extend through and are accurately fitted to slide within packingbushings 55 in the head I! and are threaded into the upper part of thepiston 20. Compression coil springs 56, disposed above the head l1 andabout the upper ends of the stud bolts 54, seat against the bushings 55and washers 51, the latter being In the structure of Fig. 5 the valvecasing. II and the cylinder block I2 are shown as being integrallyformed, merely to indicate an available variation in the valve and pressdesign. No retarding valve is employed in this structure as illustrated,although it is obvious that such a valve may be employed or not, asdesired.

The structures of Figs. 3 and 5 operate substantially alike. After theram l9 has been initially advanced by independent means (not shown),fluid is introduced, under pressure, into the valve-closing chamberI512, thus closing the valve against the tension of the coil springs(spring 44 in Fig. 3 and springs 56 in Fig. 5), and the continuedintroduction of pressure causes the check-valve 33 to open andestablishes sufficient working pressure in the chambers l5b, l5d, and IEto enable the ram I9 to perform the desired work. The aggregate downwardforce upon the top of the piston 20 and upon the upper surface of theshoulder 26 on the piston is greater than the combined upward force uponthe bottom of the piston and the force exerted by the springs 44 or 56,and hence the piston is held in its closed position while suitablepressure is maintained in the chamber. I512. The return or openingstroke of the piston 20 is accomplished by exhausting chamber i511,whereupon the springs 44 or 56 urge the piston upwardly, the chamberl5d, meanwhile, exhausting through the axial passage or passages 43 andthe ram 19 being independently raised. The opening of the valvedisclosed in Fig. 3 would be slower than that of Fig. 5, and also wouldbe cushioned because of the action of the retarding valve 45, ashereinbefore explained.

The structure illustrated in Fig. 7 differs from that of Fig. 5 only inthat the lower end area of the piston 20 is slightly greater than theupper end area thereof. It will be observed that when the piston in thisembodiment is in closed position, the fluidin chambers Hid and I6 areunder substantially uniform pressure in view of the fact that saidchambers are in communication through the vertical passage 43 and thatthe downward force exerted upon the top of the piston 2%, through thechamber l5d, would be somewhat less than the upward force exerted uponsaid piston through the chamber l6, and hence, the chamber i5d would notalone sufiice to hold the said piston in closed position. It should beobserved, however, that the sum of the areas of the piston 20 subjectedto downward force through chambers i511 and ltd is greater than the areaof the bottom of the said piston and consequently when the piston is inclosed position, the chambers ifiband EM, both being under workingpressure, operate to hold the piston in its closed position so that anadequate working pressure may be established and maintained. Wherespring means, such. as springs 56 are employed to hold the piston 20normally in an open position, the differential between the areas of thepiston 20, which are subjected to downward hydraulic force, and the areaof the bottom of the piston, which is subjected to upward hydraulicforce, should be sufficient to hold the piston 20 in closed position,not only against the hydraulic forces tending to throw it open. but alsoagainst the compressive force of said springs which likewise have 'atendency to move the piston to its open position. It will be seen thatwith this structure, when the pressure is released in the chamber l5bfor the purpose of opening the prefill valve upon the return stroke maybe achieved by the application of the principles disclosed herein in avariety of valve and press structures and that the structures employedto give eifect to such principles may be variously modified, without,however, departing from the invention and the spirit thereof, as

defined in the appended claims.

What I claim is: l

1. The combination in a hydraulic press or the like, of a source ofsupply of fluid at relatively high pressure, a source of supply of fluidat relatively low pressure, a substantially cylindrical reciprocatingvalve element having an inner end adapted to limit the flow of fluidbetween the latter source of fluid supply and an associated hydraulicpress when the valve element is in a closed position, an annularhydraulic chamber, partly defined by an intermediate circumferentialportion of said element and. adapted to coact therewith whereby to movesaid element to a closed position, and a substantially separatehydraulic chamber, partly defined by the outer end of said element andadapted to coact therewith whereby to substantially hold the saidelement in a closed position.

2. A prefill valve for hydraulic presses and the like, comprising avalve casing, a valve element accurately fitted within said casing andadapted to be reciprocated therewithin between an outer position inwhich the valve is open and an inner position'in which the valve isclosed, and the said element is subjected at its inner end to theworking pressure of fluid within the press, means for opening the valve,means for closing the valve, and means for holding the valve closed, themeans for closing the valve comprising a relatively small valve-closinghydraulic chamber, partly defined by and coacting with a portion of saidvalve element whereby to move the latter inwardly to a closed position,and the means for holding the valve closed comprising a relatively largehydraulic chamber partly defined by the outer end of the valve element,and means affording fluid communication between the outer and inner endof said valve element when the valve is closed, a relatively largerarea-of the outer end of said element than of the inner end thereofbeing adapted to receive fluid working pressure when the valve isclosed, whereby to hold the valve element in a closed position untilsaid working pressure is released.

3. A prefill valve according to claim 2, the means afiording fluidcommunication between the outer and inner end of said valve element,when the valve is closed, comprising a passage disposed within the valveelement and extending means afiording fluid communication between theouter and innerend of said valve element, when the valve is closed,comprising a passage disposed within the valve element and extending thelatter to an open position.

6. A prefill valve according to claim 2, the means for opening the valvecomprising a hydraulic chamber, partially defined by and coacting with aportion of the valve element whereby to urge the latter to an openposition.

7. A prefill valve for hydraulic presses and the like, comprising a portfor exhausting and filling a ram chamber of a press, a duct forconveying fiuid'between said port and a source of fluid supply, arelatively large pressure-balancing hydraulic chamber, a reciprocatingvalve element having an inner end adapted to seat across said portwhereby to close said port and duct against relative fluidcommunication, and said valve element, also, having an outer end partlydefining said pressure-balancing chamber, an interior passage in saidelement for exhausting and filling said latter chamber and adapted toaflord fluid communication between said latter chamber and said port,when the valve is closed, means for moving the valve element outwardlyto open the valve, and a relatively small hydraulic chamber coactingwith a part of the valve element whereby to move said. element inwardlyto close the valve, the parts of the valve element which are subjectedto inward hydraulic pressure when the valve is closed being soproportioned that the force resulting from such pressure tending to urgethe valve element to a closed position, is

greater than all coexisting forces tending to open the valve.

8. A prefill valve for hydraulic presses and the like, according toclaim 7, the said interior passage in the valve element having a valvetherein adapted to permit relatively rapidoutward flow of fluid throughsaid passage whereby to permit the rapid filling of saidpressure-balancing chamber and being further adapted to retard theinward flow of fluid through said passage whereby to retard theexhaustion of said chamber and to permit the fluid in said chamber tocushion the opening stroke of the valve element.

9. A prefill valve for hydraulic presses and the like, according toclaim 7, further characterized in having a duct adapted to afford fluidcommunication between the said relatively small chamber and the ramchamber of the press, when the valve is closed, whereby to permit theintroduction of fluid into the ram chamber through the said smallchamber.

10. A prefill valve for hydraulic presses and the like, according toclaim 7, further characterized in having a duct adapted to afiordfluid-communication between the said relatively small chamber and theram chamber of the press, when the valve is closed, whereby to permitthe introduction of fluid into the ram chamber through the said smallchamber, said latter duct having a valve, associated therewith, adaptedto permit the flow of fluid into the ram chamber only when the prefillvalve is closed.

11. A prefill valve for hydraulic presses and the like, according toclaim 7, further characterized in having a duct in the valve elementadapted to i afiord fluid communication between the said awaerorelativelysmall chamber and the ram chamber of the press, when the valveis closed, whereby to permit the introduction of fluid into the ramchamber through the said small chamber, said latter duct having a valve,associated therewith, adapted to permit the flow of fluid into the ramchamber only when the prefill valve is closed.

12. The combination with a hydraulic press having a ram chamber, a ramadapted to reciprocate within said chamber and having an interior quickadvance chamber therein, and a fixed fluid-supply pipe extending withinan axial bore in the ram and into said quick advance chamber, of aprefill valve comprising a casing within which the said pipe extends, a;surge chamber in said casing communicating with the ram chamber, anopening in said casing arranged to permit the flow of fluid into saidsurge chamber, a reciprocating valve element slidably mounted upon saidfixed pipe within said casing, a relatively small hydraulic chamber,partly defined by and coacting with a portion of the valve element andadapted to move the latter to a closed position wherein a portionthereof closes the ram chamber and surge chamber against relative fluidcommunication, and a substantially separate, relatively large hydraulicchamber, partly defined by and coacting with a portion of the valveelement and adapted to hold the latter in such closed position.

13. A hydraulic press and a prefill valve therefor comprising ahydraulic ram chamber, a passage for filling and exhausting saidchamber, a reciprocating valve element having an inner end adapted forclosing said passage, means for reciprocating said element between openand closed positions, and a hydraulic pressure balancing chamber incontinuous fluid communication with said ram chamber, the said inner endof the valve element, when said element is in closed position, beingsubject to a hydraulic force from within the ram chamber tending to movethe said valve element toward an open position, and said valve elementalso having a surface which is subject to a hydraulic force from withinthe pressure-balancing chamber substantially equal izing thefirst-mention hydraulic force and opposing the latters tendency to movethe valve element toward an open position.

14. A hydraulic press and a prefill valve therefor according to claim13, the means for moving said valve element to closed positioncomprising a separate hydraulic valve-closing chamber.

15. A hydraulic press and a prefill valve therefor, comprising ahydraulic ram chamber, a passage for filling and exhausting saidchamber, a reciprocating valve element having an inner end adapted forclosing said passage. a hydraulic pressure-balancing chamber incontinuous fluid communication with said ram chamber, a hydraulicvalve-closing chamber for moving said element from an open to a closedposition, and means for moving said element from a closed to an openposition, the said element having surfaces subject to hydraulic pressurefrom within said valve-closing and pressure-balancing chambers tendingto urge said valve element towards its closed position, and the surfaceof said inner end of the valve element beingsubject to pressure fromwithin the ram chamber, when the said element is in its closed position,tending to urge said element towards its open position, the lattersurface being of lessarea than the areas of said firstmentioned surfacesand of greater area than the area of the said surface which is subjectto pressure from within the pressure-balancing chamber.

16. The combination with a hydraulic press having a ram chamber, a ramadapted to reciprocate within said chamber and having an interiorquick-advance chamber therein, and a fixed fluidsupply pipe extendingwithin an axial bore in the ram and into said quick-advance chamber, ofa prefill valve comprising a casing within which the said pipe extends,a passage in said casing affording fluid communication between theexterior thereof and the said ram chamber, a reciprocating valve elementwithin said casing through which valve element the said pipe extends,means for moving said valve element from a closed position wherein suchfluid communication is substantially cut off to an open'position, ahydraulic valve-closing chamber adapted to impose pressure upon thevalve element tending to move it from an open position to such closedposition and 'a substantially separate hydraulic chamber adapted toimpose pressure upon the valve ele ment, when the latter is in closedposition, tending to oppose forces exerted upon said valve element-whichtend to move the latter to an open P sition.

1'7. The combination according to claim 16,

further characterized in including a passage which, when the valveelement is in closed position, affords fluid communication between saidlast mentioned hydraulic chamber and the said ram chamber.

' 18. The combination according to claim 16, further characterized inincluding a passage which, when the valve element is in closed position,aflords fluid communication between said last mentioned hydraulicchamber and the said ram chamber, the said last mentioned passageconstituting the sole means for filling and exhausting said latterchamber.

19. The combination according to claim 16, further characterized inincluding a passage in said valve element which, when the latter is inclosed position, affords fiuidcommunication between said last mentionedhydraulic chamber and the said ram chamber.

CANNON.

